The present invention relates to an electrophotographic duplication apparatus which employs a unique scanning method for duplicating operation.
Hitherto production of copies having different sizes from an original was limited to the case of producing smaller copies in only a limited number of reduced ratios because the apparatus involved was cumbersone and expensive. In order to obtain copies of the desired enlarged copies, there was only the method which comprises microphotograph-enlargement. However, this method requires much time and is expensive and very inconvenient and the size of the original to be copied has some limitation. Furthermore, in order to obtain copies of a size larger than the above described size, 1:1, copies were only obtainable from a single-faced original by a transmission-contact method. In this method, a light exposure system including magnifying means is large-sized and complicated and, consequently, the driving unit, photosensitive element, electrostatically charging unit, transferring unit and fixing unit for fixing transferred sheets also must be large-sized. Obtaining copies having this large size is difficult from the viewpoint of enlarging the known small-sized electrophotographic duplicating apparatus because more rigorous conditions are required for each unit and element. Consequently, it is difficult to use this method in a field where obtaining copies of original such as drawings or maps requires accuracy.
For example, when an original of DIN AO size (841mm .times. 1189mm) is copied by the above transmission-contact method where the original laying unit and the image transmission system including the magnifying (projecting) lens are both stationary with each other during the copying operation, the projecting lens must cover at least a diagonal line (about 1360mm) of the original for completing the desired copying operation so that the projecting lens having substantially a long focal length is required resulting in the duplicating apparatus of a large-sized construction. Futher, the conventional electrophotographic duplicating apparatus has the following other disadvantages.
(i) Photosensitive elements commonly used in electrophotography such as selenium or zinc oxide photosensitive element, and so on have the limitation that the surface of the element is very easily injured. Accordingly, it is necessary to rub the surface of the photosensitive element softly, slowly and uniformly at a suitable speed to improve the development of the images per unit of time and area. In order to develop the images, there has been a cascade process and a magnetic brush process. Until now there has not been any improvement in the brush process to provide excellent, uniform images, namely, in the device whereby latent images change into visible images, including the area where the photosensitive element contacts the developer.
(ii) In order to carry out charging and transferring by an electrophotographic apparatus, both ends of the corona wires are fixed and direct voltage is applied thereto and the surface of the photosensitive element is subjected to corona discharging. In such an arrangement where only the ends of the corona wires are supported, the application of electric voltage causes them to bend toward the surface of the photosensitive element causing vibration. Therefore, the distance between the surface of the photosensitive element and the corona wires can not be kept constant and this causes uneven charging and spark discharging sometimes occurs. This is the result of the fact that the corona wires are supported only at their ends.
(iii) In the electrostatic transfer method, in order to make a copy it is necessary that the entire transfer sheet be brought into contact with the entire surface of the photosensitive element. Images corresponding to the original are transferred to the transfer sheet by corona discharging on one side of the transfer sheet. However, the transfer sheet does not come in close contact with the surface of the photosensitive element because air gaps are formed between the surface of the photosensitive element and the transfer sheet due to the strain on the transfer sheet. Consequently, images corresponding to the original images can not be transferred. In order to prevent this defect, transfer sheets are packed previously in moisture-proof packaging. However, they are exposed to another atmosphere when the package is opened for use, and generating strain on the transfer sheet can not be prevented. Furthermore, in a conventional electrostatic duplication apparatus, which is a small-size copying apparatus for forming relatively small-sized copies such as B-4 or A-4 size, strain is not a problem because the transfer sheets used are small-sized. However, when using large-sized transfer sheets such as those greater than A-2 size, strain increases in proportion to the area and the resulting transfer images do not correspond to the original images.
Accordingly, it is an object of the present invention to provide an electrophotographic duplication apparatus which can resolve the above described defects, which is small-sized and in which the magnification or reduction ratio is changeable at will at the time of duplication.
It is another object of the present invention to provide an electrophotographic duplication apparatus which includes a unique combination of an original laying unit and an image transmission system wherein the image transmission system whih comprises a focusing light path, a duplication light path and a magnifying mechanism moves toward an original laying unit by scanning the image of an original layed on the above unit section by section and furthermore the original laying unit is also movable simultaneously in either same or opposite direction relative to the movement of the image transmission system so that an image of a desired magnification rate and of accuracy is produced on a photosensitive element without requiring the magnifying lens of a long focal length which is inevitable in a conventional electrophotographic duplication apparatus for copying the original having the considerable size such as DIN AO (841 mm .times. 1189 mm).
It is still another object of the present invention to provide an electrophotographic duplication apparatus by which uniform discharging is carried out by stretching a fine linear insulator across the corona wires to prevent vibration of the corona wires so as that the distance between the photosensitive element and the corona wires is constant.
A further object of the present invention is to provide a developing device which is characterized by heteropolar permanent magnet rods which are disposed adjacently with alternating polarities on a fixed non-magnetic axis having at least one blank area in which no magnet is placed between the magnet rods, a fixed permanent magnet rod disposed so that it faces the heteropolar permanent magnet rods with the opposed faces of the facing magnetic rods having a different polarity from each other, the development of images being carried out between the facing magnet rods by movement of a non-magnetic plate, the photosensitive element having a photoconductive layer, a developer and a non-magnetic plate. Furthermore, it is characterized by a guide plate which provides a suitable place in which the developer is able to move, whereby the developer is rubbed and agitated up and down and left and right.
A still further object of the present invention is to provide an apparatus in which transfer sheets are not subject to strain and are able to come into uniformly close contact with the surface of the photosensitive element.
A still further object of the present invention is to provide an electrophotographic duplication apparatus in which copies having the desired magnification or reduction ratio can be produced from an original such as large-sized original, small-sized original, stereographic original, sheet original, one-face printed original or both-face printed original, and so on.